I got the HEQ5 pinouts from a couple of docs I had here on the PC, one was for a DIY Bluetooth interface, and its schematic showed 5,4,3 for gnd, TD, RD resp. I suspect it's wrong. Then the Synscan manual I had, fig n Page 10, showed the pinout on the base of the handbox (which should be mirrored at the other end of the RJ11 cable) as 2 TD, 5 RD, 3&4 Gnd, 1 & 6 NC.
I posted that, but after seeing your prior post, I though it was probably too confusing and uncertain, so decided to let it slide until we hear from Adam again
Cheers. You'll love the controller!